Friction material composition and friction material using the same

ABSTRACT

There are disclosed a friction material composition which comprises a fibrous material except for asbestos, an inorganic friction regulator, an organic friction regulator and a binder, part of the inorganic friction regulator is α alumina and γ alumina in combination, a weight ratio of the α alumina and the γ alumina, α alumina:γ alumina, is in the range of 1:20 to 1:5, and part or whole part of the binder is a silicon-containing phenol resin, and a friction material obtained by molding the friction material composition under heating and pressure.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a friction material compositionsuitable for the production of friction materials such as disc brakepads or brake linings to be used to brake cars, and a friction materialusing the same.

[0003] 2. Description of the Related Art

[0004] Friction materials such as disc brake pads and brake linings areused to braking cars. Friction materials mainly used at present areNon-Asbestos Organic (hereinafter abbreviated to as “a NAO material”)series disc brake pads, which, as disclosed in Japanese UnexaminedPatent Publications No. Hei. 2-132175A and No. Hei. 6-184525A, contain afriction regulator including fibrous materials such as Aramid fiber,inorganic fiber, etc., cashew dust, graphite and the like to cause lesssqueal noise or less groan noise.

[0005] However, required performances to the brake in recent years aretend to be increased more and more, in particular, further improvementin effectiveness of the braking and noise and vibrations (groan noise,squeal noise, vibrations, etc.) are required. In the disc brake padscomprising the above-mentioned NAO material, it is required to improveeffectiveness of braking under high load, high speed, high temperature,etc.

[0006] Also, when a driver is to decrease a speed of a car by pedaling abrake pedal, if there is a tendency of increasing effectiveness ofbraking with a lapse of a braking time (hereinafter referred to as “afriction coefficient (μ) build up”) even when a pedaling power is madeconstant, it is preferred since the driver feels secure.

[0007] However, when a case in which, for example, braking is carriedout with a constant pedaling powder from an automobile speed of 50 km/his considered, it is preferred to exist μ build up during braking from acar speed of 50 km/h to about 20 km/h. On the other hand, during a carspeed of 20 km/h to immediately before stop of 0 km/h, the μ build up isconsidered to be preferably moderate or none in view of expectinginhibition of occurrence of groan noise or squeal noise.

[0008] Here, there is a means to add a polishing agent having higherMohs' hardness to the conventional disc brake pad comprising a NAOmaterial to obtain μ build up. In such a case, the μ build up continuesimmediately before stop, so that there is a tendency of easily occurringgroan noise or squeal noise.

[0009] Moreover, one of the problems in recent years with regard to theabove-mentioned noise and vibrations, when an automobile is allowed tostand for more than several hours and braking is carried out after thebrake was cooled to an atmospheric temperature and moisture-adsorbed,effectiveness of the brake is easily increased by braking with theinitial several times (hereinafter referred to as “μ increase afterallowing to stand”). At that time, there are cases in which squeal noiseoccurred (hereinafter referred to as “cold squeal noise”), and this isrequired to be improved.

[0010] In FIG. 1 and FIG. 2, μ build up is shown in the relationshipbetween a braking time and μ. Of these, FIG. 1 shows μ build up of aconventional product, and FIG. 2 shows μ build up in an ideal form. Inboth of FIGS. 1 and 2, increase in μ relative to a braking time isobserved, but in FIG. 1, μ build up continues immediately before stop,and there are tendency of easily causing groan noise or squeal noise. Tothe contrary, in FIG. 2, during an automobile speed of 20 km/h toimmediately before stop of 0 km/h, the μ build up shows moderatebehavior and occurrence of groan noise or squeal noise is a little.

SUMMARY OF THE INVENTION

[0011] The present invention is to provide a friction materialcomposition which is less lowered in effectiveness under high load, highspeed, high temperature, etc., excellent in stability of μ, fadingresistance and μ build up, causing less occurrence of cold squeal noiseby controlling increase in μ after allowing a car for a long time, andsuitable for a friction material.

[0012] The present invention is also to provide a friction materialcomposition particularly excellent in stability of μ, fading resistanceand μ build up, and suitable for a friction material, among theinvention of Claim 1.

[0013] The present invention is further to provide fiction materialsexcellent in stability of μ, fading resistance and μ build up, andcausing less occurrence of cold squeal noise.

[0014] The present invention relates to a friction material compositionwhich comprises a fibrous material except for asbestos, an inorganicfriction regulator, an organic friction regulator and a binder, part ofthe inorganic friction regulator is α alumina and γ alumina incombination, a weight ratio of the α alumina and the γ alumina (αalumina:γ alumina) is in the range of 1:20 to 1:5, and part or wholepart of the binder is a silicone-containing phenol resin.

[0015] Also, the present invention relates to a friction materialcomposition comprising α alumina and γ alumina in a total amount thereofbeing 1 to 10% by weight based on the whole content of the frictionmaterial composition.

[0016] Moreover, the present invention relates to a friction materialobtained by molding the above friction material composition underheating and pressure.

[0017] Furthermore, the present invention relates to a friction materialin which the above-mentioned friction material is a disc brake pad orbrake linings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a graph showing μ build up of the conventional materialwith the relationship between a braking time and μ.

[0019]FIG. 2 is a graph showing μ build up of an ideal material with therelationship between a braking time and μ.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The friction material composition of the present inventioncomprises a fibrous material except for asbestos, an inorganic frictionregulator, an organic friction regulator and a binder, and part of theinorganic friction regulator contains α alumina and γ alumina. Theweight ratio of the α alumina and the γ alumina (α alumina:γ alumina) isset in the range of 1:20 to 1:5, preferably 1:17 to 1:8, more preferably1:15 to 1:10. If the weight ratio of the α alumina exceeds 1:5, build upof μ continues immediately before stop and squeal noise or low frequencygroan noise is likely generated. On the other hand, if the ratio of theα alumina becomes less than 1:20, then, build up of μ tends to beinsufficient.

[0021] A total content of the α alumina and the γ alumina is preferablyin the range of 1 to 10% by weight based on the total content of thecomposition, more preferably in the range of 2 to 9%, further preferablyin the range of 3 to 8% by weight. If the total content thereof is lessthan 1% by weight, effectiveness of braking under high load, high speed,high temperature, etc. is lowered, and fading resistance tends to beworsened, while if it exceeds 10% by weight, squeal noise or groan noisetends to be easily generated. The α alumina to be used in the presentinvention may include, for example, corundum and having a latticeconstant a=5.14 Å, and the γ alumina to be used in the present inventionmay include, for example, active alumina, that has a spinel typestructure with a lattice defect and has a lattice constant a=7.75 to8.08 Å.

[0022] In the present invention, it is one of the characteristicfeatures that part or whole part of the binder comprises asilicone-containing phenol resin. The phenol resin to be used in thepresent invention is a thermosetting resin obtained by condensing aphenol derivative and an aldehyde derivative in the presence of an acidor an alkali. When the silicone-containing phenol resin is not used, ifthe resulting friction material is, for example, a brake disc pad, afriction coefficient is greatly increased at a low speed after allowingto stand for a long time or under low speed-decreasing conditions (20km/h, 0.2 G), whereby cold squeal noise frequently occurs. As thesilicone-containing phenol resin, a phenol resin in which silicone oilis dispersed or modified with silicone oil, a phenol resin containingsilicone rubber, etc. is preferably used. The silicone-containing phenolresin is preferably contained in the total composition in the range of 2to 15% by weight, more preferably 4 to 13% by weight. As thesilicone-containing phenol resin, for example, RX2325C (trade name,available from Mitsui Chemicals, etc. may be mentioned. When siliconeoil is added to the phenol resin, an amount thereof is 1 to 20% byweight based on the whole amount of the silicone-containing phenol resinand when silicone rubber is contained in the phenol resin, an amountthereof is 1 to 30% by weight based on the same.

[0023] The material to be used in the present invention includes, inaddition to the above-mentioned α alumina, γ alumina andsilicone-containing phenol resin, conventionally known materials in theart, for example, fibrous materials such as copper fiber, bronze fiber,phosphor bronze fiber, Aramid fiber, acrylic fiber, carbon fiber,ceramic fiber, rock wool, potassium titanate fiber, calcium carbonatewhisker, magnesium carbonate whisker, etc.; inorganic frictionregulators such as barium sulfate, calcium carbonate, magnesiumcarbonate, calcium oxide, calcium hydroxide, vermiculite, mica,wollastonite, alumina other than α and γ, silica, zirconia, zircon,magnesia, iron oxide, iron sulfate, tin sulfate, antimony trisulfide,molybdenum disulfide, carbon black, corks, etc.; organic frictionregulators such as various kinds of rubber powders, cashew dust, etc.;binders including thermosetting resins such as melamine resin, polyimideresin, furan resin, etc., and an elastomer-modified phenol resin, etc.,and depending on necessity, metal powders such as copper powder, bronzepowder, zinc powder, etc.

[0024] A content of the above-mentioned fibrous material is preferably 5to 40% by weight, more preferably 10 to 35% by weight, furtherpreferably 15 to 30% by weight based on the total amount of thecomposition in the point of mechanical strength, etc. A content of theinorganic friction regulator is preferably 20 to 80% by weight, morepreferably 30 to 70% by weight, further preferably 40 to 60% by weightbased on the total amount of the composition depending on thecharacteristics thereof. A content of the organic friction regulator ispreferably 2 to 25% by weight, more preferably 4 to 23% by weight,further preferably 6 to 21% by weight based on the total amount of thecomposition in the point of an abrasion amount of a pair material. Acontent of the binder is preferably 2 to 15% by weight, more preferably3 to 14% by weight, further preferably 4 to 13% by weight based on thetotal amount of the composition in the points of mechanical strength andwear resistance.

[0025] These materials are formulated so that the total compositionbecomes 100% by weight.

[0026] The friction material of the present invention can be prepared bymixing the above-mentioned materials (the friction material composition)uniformly, subjecting the mixture to provisional molding (i.e., a greencompact), inserting the green compact and a backing plate into a mold,subjecting to molding by a molding method under heating and pressure,and then subjecting to a post-heating treatment, and, if necessary, bysubjecting to a scorching treatment to remove an organic material on thesurface of the molded product.

[0027] Incidentally, a heating temperature at the time of molding ispreferably 130 to 170° C., more preferably 140 to 160° C. A pressure ofthe same is preferably 20 to 60 MPa, more preferably 30 to 50 MPa. Atemperature for the post-heating treatment is preferably 180 to 300° C.,more preferably 200 to 250° C. Also, the scorch treatment is carried outby a method of pressing a hot press to a friction member material, amethod of heating with direct fire such as flame of a gas, a method ofheating with a radiant heat such as far infrared rays, etc., and it isnot specifically limited. With regard to the conditions for the scorchtreatment, it may be selected and carried out by electing conditionsdepending on the materials to be used.

EXAMPLES

[0028] In the following, the present invention will be explained byreferring to Examples.

Examples 1 to 5

[0029] By formulating the materials shown in Table 1, and mixing thesame by a mixer with a rotation number of 3000 r/min for 4 minutes toobtain friction material compositions. Then, these friction materialcompositions were provisionally molded to a predetermined shape,inserting the green compact and a back mold in a mold, subjecting tomolding under heating and pressure with the conditions of 140° C.±5° C.and 50 MPa for 10 minutes, and further subjecting to post-heatingtreatment at 230° C. for 5 hours, and polishing the same after coolingto obtain disc brake pads, respectively.

Comparative Examples 1 to 5

[0030] In the same manner as in Examples 1 to 5 except for changing theformulations thereof as shown in Table 2, disc brake pads were obtained.TABLE 1 (unit: % by weight) Item Example 1 Example 2 Example 3 Example 4Example 5 Binder Silicone-containing Phenol resin, RX2325C 9 9 9 9 4trade name, available from Mitsui Chemicals Inc. Phenol resin, HP-491UP,trade name, — — — — 5 available from Hitachi Chemical Co., Ltd. FibrousAramid resin (Kevlar ® resin) available 3 3 3 3 3 material from DuPont-Toray Co., Ltd. Potassium titanate resin 7 7 7 7 7 Rock Wool 7 7 77 7 Copper fiber 17 17 17 17 17 Inorganic Antimony trisulfide 4 4 4 4 4friction Graphite, G-70, trade name, available 6 6 6 6 6 regulator fromK. K. Chuetsu Graphite Kogyosho Zircon sand 8 8 8 8 8 Barium sulfate18.5 14 18 23 18.5 Mica 7 7 7 7 7 α alumina powder, available from Showa0.5 0.5 1 0.1 0.5 Denko K. K., maximum particle size: 50 μm or less γalumina powder, available from Mizusawa 5 9.5 5 0.9 5 ChemicalIndustries, Ltd. maximum grain size: 150 μm or less Organic Cashew Dust,H101, trade name, available 5 5 5 5 5 friction from Cashew K. K.regulator Rubber powder, NBR powder 3 3 3 3 3

[0031] TABLE 2 (unit: % by weight) Comparative Comparative ComparativeComparative Comparative Reference Reference Item example 1 example 2example 3 example 4 example 5 example 1 example 2 BinderSilicone-containing Phenol resin, — — 9 9 — 9 9 RX2325C trade name,available from Mitsui Chemicals Inc. Phenol resin, HP-491UP, trade name,9 9 — — 9 — — available from Hitachi Chemical Co., Ltd. Fibrous Aramidresin (Kevlar ® resin) available 3 3 3 3 3 3 3 material from DuPont-Toray Co., Ltd. Potassium titanate resin 7 7 7 7 7 7 7 Rock Wool 77 7 7 7 7 7 Copper fiber 17 17 17 17 17 17 17 Inorganic Antimonytrisulfide 4 4 4 4 4 4 4 friction Graphite, G-70, trade name, available6 6 6 6 6 6 6 regulator from K. K. Chuetsu Graphite Kogyosho Zircon sand8 8 8 8 8 8 8 Barium sulfate 23.1 13 19 15.8 18.5 23.1 13 Mica 7 7 7 7 77 7 α alumina powder, available from Showa 0.1 1 1 0.2 0.5 0.1 1 DenkoK. K., maximum particle size: 50 μm or less γ alumina powder, availablefrom 0.8 10 4 8 5 0.8 10 Mizusawa Chemical Industries, Ltd. maximumgrain size: 150 μm or less Organic Cashew Dust, H101, trade name, 5 5 55 5 5 5 friction available from Cashew K. K. regulator Rubber powder,NBR powder 3 3 3 3 3 3 3

[0032] Next, with regard to the disk brake pads (friction materials) ofthe present invention and those of Comparative examples, effectiveness,μ build up and cold squeal noise were measured. The results are shown inTable 3. Incidentally, the test conditions are as mentioned below.

[0033] (1) Effectiveness and Cold Squeal Noise

[0034] A dynamo test was carried out according to a car brake apparatusdynamo meter testing method by JASO C406-87, and an average μ underusual conditions (50 km/h, 0.3 G), an average μ under high speed andhigh speed-reducing conditions (180 km/h, 0.6 G), and a minimum μ at thefirst fading test were compared to each other.

[0035] Moreover, after completion of the test by JASO C406-87, the testmachine was allowed to stand under the conditions at 5° C. and 40% RH(relative humidity), and after allowing to stand, braking test wascarried out for 15 times under low speed and low speed-reducingconditions (20 km/h, 0.2 G). An increased amount of μ after allowing tostand was obtained from the difference between μ at the first timebraking and μ under the usual conditions (50 km/h, 0.3 G), and furtherfrequency of occurrence of cold squeal noise was compared to each other.

[0036] (2) μ Build Up

[0037] An actual test was carried out by using a FF car (class of 2500cc displacement) manufactured by Nissan Motor Co., Ltd. In a brakingtest with a constant pedaling power aiming at a car speed of 50 km/h andan initial speed-reducing rate of 0.2 G, an amount of the μ build up wasmeasured from increase in speed-reducing rate relative to the brakingtime. At this time, an amount of the μ build up from a car speed of 50km/h to 20 km/h and an amount of the μ build up from a car speed of 20km/h to 0 km/h were calculated. TABLE 3 Dynamo test resultsEffectiveness High temp. level after Usual High speed effectivenessallowing to Cold effectiveness effectiveness level stand squeal Actualcar level level (First time (20 km/h, noise test results (50 km/h, (180km/h, fading) 0.2 G) (Average (Frequency μ build up μ build up 0.3 G)0.6 G) (Lowest μ value of causing (50→20 km/h) (20→0 km/h) (average μ(average μ value of at first time squeal (increased (increased value)value) average μ) braking) noise) (%) amount of μ) amount of μ) Example1 0.46 0.43 0.41 0.56 0 0.026 0.014 Example 2 0.49 0.45 0.43 0.54 00.022 0.012 Example 3 0.49 0.43 0.40 0.57 0 0.035 0.026 Example 4 0.450.40 0.38 0.58 0 0.018 0.005 Example 5 0.47 0.42 0.40 0.59 6.7 0.0220.013 Comparative 0.45 0.37 0.35 0.68 26.7 0.017 0.006 example 1Comparative 0.50 0.45 0.42 0.64 53.3 0.043 0.029 example 2 Comparative0.48 0.42 0.40 0.56 0 0.032 0.040 example 3 Comparative 0.47 0.44 0.430.55 0 0.009 0.007 example 4 Comparative 0.46 0.42 0.40 0.68 66.7 0.0200.010 example 5 Reference 0.45 0.38 0.36 0.59 6.7 0.017 0.006 example 1Reference 0.50 0.45 0.42 0.61 33.3 0.043 0.029 example 2

[0038] The judgment standard in Table 3 is as follows:

[0039] An average friction coefficient under high speed and highspeed-reducing conditions (180 km/h, 0.6 G), the lowest frictioncoefficient at the time of first fading test and the amount of the μbuild up from a car speed from 50 km/h to 20 km/h in an actual car testmean that a larger numerical value is good, and the numerals of theamount of the μ build up with a car speed from 20 km/h to 0 km/h, anincreased amount of the μ after allowing to stand and frequency ofoccurrence of cold squeal noise show that a smaller number means good.

[0040] Incidentally, the frequency of occurrence of cold squeal noisewas obtained by the following equation.

Frequency of occurrence of cold squeal noise (%)={(Number of occurrenceof squeal noise)/(Number of braking)}×100

[0041] As shown in Table 3, it would be clear that the disc brake padsof Examples according to the present invention are high in effectivenessunder the high speed and high speed-reducing conditions (180 km/h, 0.6G) and fading conditions. Also, it would be clear that the amount of theμ build up with a car speed from 20 km/h to 0 km/h is repressed to alower value than the amount of the μ build up with a car speed from 50km/h to 20 km/h, increase in the friction coefficient under the lowspeed and the low speed-reducing conditions (20 km/h, 0.2 G) afterallowing to stand is a little and frequency of occurrence of cold squealnoise is low.

[0042] To the contrary, in the disc brake pad of Comparative example 1,effectiveness under the high speed and high speed-reducing conditions(180 km/h, 0.6 G) and fading conditions are low, and increase in thefriction coefficient under the low speed and the low speed-reducingconditions (20 km/h, 0.2 G) after allowing to stand is large. In thedisc brake pads of Comparative examples 2 and 5, increase in thefriction coefficient under the low speed and the low speed-reducingconditions (20 km/h, 0.2 G) after allowing to stand is large. In thedisc brake pad of Comparative example 3, the amount of the μ build upwith a car speed from 20 km/h to 0 km/h is larger than the amount of theμ build up with a car speed from 50 km/h to 20 km/h, so that groan noiseor squeal noise is likely caused. Moreover, in the disc brake pad ofComparative example 4, there is a problem that the amount of the μ buildup with a car speed from 50 km/h to 20 km/h was insufficient.

[0043] Incidentally, in the disc brake pad of Reference example 1 inwhich α alumina and γ alumina were contained in an amount of 0.9% byweight based on the total amount of the whole composition, it showed aslightly lower effectiveness under the high speed and highspeed-reducing conditions (180 km/h, 0.6 G) and fading conditions ascompared with the disc brake pads of Examples of the present invention,but are higher than those of Comparative example 1. Also, in the discbrake pad of Reference example 1 in which α alumina and γ alumina werecontained in an amount of 11% by weight based on the total amount of thewhole composition, it showed a slightly larger increase in the frictioncoefficient under the low speed and the low speed-reducing conditions(20 km/h, 0.2 G) after allowing to stand as compared with the disc brakepads of Examples of the present invention, but is lower than that ofComparative example 2.

[0044] The friction material composition according to the presentinvention is a little in lowering of effectiveness under high load, highspeed, high temperature, etc., excellent in stability of μ, fadingresistance and μ build up, causing less occurrence of cold squeal noiseby controlling increase in μ after allowing a car for a long time, andsuitable for a friction material.

[0045] The friction material composition according to the presentinvention is particularly excellent in stability of μ, fading resistanceand μ build up, and suitable for a friction material, among the abovecomposition.

[0046] The fiction materials according to the present invention areexcellent in stability of μ, fading resistance and μ build up, andcausing less occurrence of cold squeal noise, so that they are extremelysuitable for industry.

1. A friction material composition which comprises a fibrous materialexcept for asbestos, an inorganic friction regulator, an organicfriction regulator and a binder, part of the inorganic frictionregulator is α alumina and γ alumina in combination, a weight ratio ofthe α alumina and the γ alumina, α alumina:γ alumina, is in the range of1:20 to 1:5, and part or whole part of the binder is asilicon-containing phenol resin.
 2. The friction material compositionaccording to claim 1, wherein a total amount of the α alumina and the γalumina is 1 to 10% by weight based on the whole content of the frictionmaterial composition.
 3. A friction material which is obtained bymolding the friction material composition according to claim 1 underheating and pressure.
 4. A friction material which is obtained bymolding the friction material composition according to claim 2 underheating and pressure.
 5. The friction material according to claim 3,wherein the friction material is a disc brake pad or brake linings. 6.The friction material composition according to claim 1, wherein theweight ratio of the α alumina and the γ alumina is in the range of 1:17to 1:8.
 7. The friction material composition according to claim 1,wherein the weight ratio of the α alumina and the γ alumina is in therange of 1:15 to 1:10.
 8. The friction material composition according toclaim 2, wherein the total amount of the α alumina and the γ alumina is2 to 9% by weight based on the whole content of the friction materialcomposition.
 9. The friction material composition according to claim 2,wherein the total amount of the α alumina and the γ alumina is 3 to 8%by weight based on the whole content of the friction materialcomposition.
 10. The friction material composition according to claim 2,wherein the silicon-containing phenol resin is at least one phenol resinselected from the group consisting of a phenol resin in which siliconeoil is dispersed, a phenol resin modified by silicone oil, a phenolresin containing silicone rubber.
 11. The friction material compositionaccording to claim 2, wherein the silicon-containing phenol resin iscontained in an amount of 2 to 15% by weight based on the whole contentof the friction material composition.
 12. The friction materialcomposition according to claim 2, wherein the silicon-containing phenolresin is contained in an amount of 4 to 13% by weight based on the wholecontent of the friction material composition.
 13. The friction materialcomposition according to claim 1, wherein the fibrous material iscontained in an amount of 5 to 40% by weight, the inorganic frictionregulator is contained in an amount of 20 to 80% by weight, the organicfriction regulator is contained in an amount of 2 to 25% by weight andthe binder is contained in an amount of 2 to 15% by weight based on thewhole content of the friction material composition.
 14. The frictionmaterial composition according to claim 1, wherein the fibrous materialis contained in an amount of 10 to 35% by weight, the inorganic frictionregulator is contained in an amount of 30 to 70% by weight, the organicfriction regulator is contained in an amount of 4 to 23% by weight andthe binder is contained in an amount of 3 to 14% by weight based on thewhole content of the friction material composition.
 15. The frictionmaterial composition according to claim 1, wherein the fibrous materialis contained in an amount of 15 to 30% by weight, the inorganic frictionregulator is contained in an amount of 40 to 60% by weight, the organicfriction regulator is contained in an amount of 6 to 21% by weight andthe binder is contained in an amount of 4 to 13% by weight based on thewhole content of the friction material composition.
 16. The frictionmaterial according to claim 3, wherein the molding is carried out at atemperature of 130 to 170° C. and a pressure of 20 to 60 MPa.
 17. Thefriction material according to claim 3, wherein the molding is carriedout at a temperature of 140 to 160° C. and a pressure of 30 to 50 MPa.